With respect to a semiconductor integrated circuit (LSI), higher performance and higher integration due to miniaturization of circuit patterns have progressed. Currently, the line width of a smallest circuit pattern of an advanced LSI is 30 nanometers (nm) or less, and it is necessary to exactly manage a circuit dimension (for example, with the accuracy of the tolerance of a variation in a dimension being 10% or less of a designed value) in order to ensure the performance of the LSI. A scanning electron microscope (SEM) is now widely used to measure the circuit dimension. NPL 1 discloses an electric field emission-type electron microscope (CD-SEM: Critical Dimension SEM) dedicated to circuit dimension measurement for observing a wafer from an upper surface thereof.
The CD-SEM is used for measuring various features as well as the line width measurement of a semiconductor circuit. For example, it has been known that roughness called line edge roughness (LER) is present in the edge of the circuit pattern, which adversely affects the circuit performance. The CD-SEM is widely used for the measurement of the LER, and for example, PTL 1 discloses a measurement method thereof.
Meanwhile, there is a demand for a solid shape of an element structure formed on a wafer through lamination and patterning processes. In particular, it is desirable to perform observation in a non-destructive manner without depending on the cross-section observation in an LSI mass production process, and an AFM or an optical method (scatterometry) is generally used as a method therefor.
The AFM is a method for measuring the shape of roughness on a sample surface by scanning the sample surface by using a probe with a fine tip in such a manner that atomic force between the tip of the probe and the sample surface is constant. The details thereof are described, for example, in PTL 2.
The scatterometry estimates the cross-sectional shape of a solid structure, by measuring the wavelength of the reflected and diffracted light or diffraction angle dependency by applying light to a pattern having a periodic solid structure, and comparing the measured dependency with a diffraction angle dependency that is obtained in advance through calculation for various cross-sectional shapes. The scatterometry is described in, for example, NPL 2.
There is a model-based library (MBL) method as a method similar to scatterometry, which estimates a cross-sectional shape using the SEM. The MBL method estimates a cross-sectional shape of a solid structure by comparing a secondary electron intensity distribution of the detection signal obtained by scanning a sample with converged electron beams, with a secondary electron signal intensity distribution that is obtained in advance through calculation for various cross-sectional shapes. The MBL is described in, for example, PTL 3 or NPL 3.
In addition, a tilt-SEM can be used as a method for measuring a solid structure using a SEM. This method estimates a three-dimensional shape according to a principle of a stereoscopic image, from a plurality of images obtained by applying electron beams to the wafer from different angles. The tilt-SEM is described in, for example, PTL 4.